Effect of modified atmosphere packaging on postharvest physiology and quality of ‘Xinli No.7 ’ pears during storage

Abstract：【Objective】The objective of this study is to optimize packaging bags and provide a scientific foundation for exploring a simple and efficient new preservation technology of‘Xinli No.7’pears during storage by studying the effect of modified atmosphere packaging and on postharvest physiology and quality.【Methods】Storage experiments with commercially mature‘Xinli No.7’pears were respectively used in sealed 0.02 mm thickness PE film bags , sealed 0.03 mm thickness PE film bags, sealed 0.04 mm thickness PE film bags and sealed 0.05 mm thickness PE film bags. These bags were spontaneously formed into an atmosphere-controlled environment and stored at a temperature of (0±0.5) ℃ and a relative humidity of 90% - 95%, and the unsealed 0.02 mm PE packaging bag was as a control. The O2 and CO2 in different bags were regularly monitored. After 120, 180 and 240 days of cold storage, the fruits were taken out and placed under 20 ℃, and fruit firmness (FF), total soluble solids (TSS), titratable acidity (TA), vitamin C (VC), L*, h° and chlorophyll fluorescence parameters of Peel and aldehyde in the stored fruits were investigated at 0 and 7 days after cold storage. Respiration rate were measured during shelf time. Decay rate and stalk preservation index in different periods of storage were calculated. Variance analysis of related data was carried out by SPSS 22.0 software.【Results】The concentrations of O2 and CO2 in sealed bagsreached equilibrium on the 30th day. The O2 volume fractions in the 0.02 mm thickness PE bags, 0.03 mm thickness PE bags, 0.04 mm thickness PE bags and 0.05 mm thickness PE bags are respectively 19.4%, 16.2%, 15.4%, 15.0%. The CO2 volume fraction of 0.02 mm thickness PE bags, 0.03 mm thickness PE bags, 0.04 mm thickness PE bags and 0.05 mm thickness PE bags are 0.5%, 2.0%, 2.6% and 3.0%, respectively. The ability level of gas adjustment was 0.05 mm thickness PE bags, 0.04 mm thickness PE bags, 0.03 mm thickness PE bags, 0.03 mm thickness PE bags from high to low in turn. And the thicker the bag thickness, the shorter the time it takes for the gas components in the bag to reach equilibrium. Modified atmosphere packaged can reduce the yellowing rate of the peel and play a better green keeping effect. The L value indicates brightness. The larger the L value, the brighter the color of the peel. The h° value is the chromaticity angle, which indicates the change in yellow-green. The higher the value, the greener the peel. When the h value reaches 90, it is considered to be completely yellow. The results of indicators showed that the adopted packaging bags slowed down the rise of L value of peel and the decline of h° value. On the (120+7) days, the L value, h° value were significantly different between treatment and control groups (p ＜ 0.05). There were no significant differences in Fo values between the treatments and controls when refrigerated for (120+7) days, 180 days, (180+7) days, 240 days, and (240+7) days. The values of Fv and Fm of the control and treatment gradually decreased from 120 days to 240 days. With the extension of refrigerated time, the Fv/Fm value of‘Xinli No. 7’fruit gradually decreased, and the Fv/Fm value increased during shelf life. There was no significant difference in Fv/Fm values between the control and treatment at 120 days and 180 days, but the Fv/Fm values of each treatment were significantly higher than the control at 240 days. On 120 days,180 days and 240 days, the fruit decay rate was significantly lower than the controlof the filmbags and improved stalk preservation index, 0.03 mm PE film bags has the lowest fruit decay rate, 0.05 mm PE film bags has the best stalk preservation index. Fruit firmness, total soluble solids and titratable acidity did not change significantly during storage of each treatments, but vitamin C content decreased significantly during storage of 0.04 mm PE film bags and 0.05 mm PE film bags. No browning was found in the flesh and core of‘Xinli No. 7 ’during the whole storage period, no matter control or treatment. No ethanol content was detected in the fruit of‘Xinli No. 7’, and the acetalde content was very low.【Conclusion】Fruits of‘Xinli No.7’more embodied in the storage period by using 0.03 mm thickness PE film bags for modified atmosphere packaging, and the O2 and CO2 concentrations in bags played a main role, and when maintained O2 at 15.3% to 16.9% and CO2 at 1.8% to 2.1% had a good preservation effect on keeping green, but reduced the quality of the fruit such as vitamin C. Therefore, it is necessary to combine modified atmosphere packaged with 1-MCP treatments, thereby achieving the goal of preservation effect.